Neighbourhood Watch is alerting its members in the area to an incident yesterday in the town centre.
A warning notice says:
"During the morning of Thursday 12 September a male person was approached by two females of Asian origin in Llangollen town centre.
"They persuaded the male to sign a petition, asking that he verified his details and confirmed his identity using a bank card.
"The male removed his bank card from his wallet to confirm his identity and later found that £30 cash was missing from the wallet.
"It is believed that these two females may have been responsible for the theft of the cash.
"If you have any information about this incident, please call North Wales Police on 101 quoting the reference number P151917."